The Amazing And Weird Maxell P-13 FM Transmitter

This transmitter has been the subject
of discussions before.

I just thought I would mention a little
experiment with mine that came about
unexpectedly.

This transmitter has been the subject
of discussions before.

I just thought I would mention a little
experiment with mine that came about
unexpectedly.

The FCC ID of the Maxell P-13 is WKA-MCAP-13.

So it is certified. I don't think the P-13 is being
made anymore, but I could be wrong.

Although it's audio curve is a little weird, and I
don't think it gets quite up to 100 percent
deviation, it doesn't sound too bad, as far as
I'm concerned.

I have a Sony IC voice recorder, you know, like
a cassette recorder without tapes. Model, ICD-BX112.

As it turns out, this little recorder is not only good
for voice, but music sounds great on it, too. It
has an external mike input, so I made an attenuator
network and recorded some old jazz on it just for
fun. The sampling rate at the highest setting is
192 kbaud/sec, if I'm correct - and I've probably
mentioned this before. Good for music.

So I plugged the P-13 transmitter into the earphone
output of the Sony recorder, and my wife and I listened
so some old jazz in the car for a while. It sounded
quite good on the car radio on 88.3 MHz. (She was
taking me to work at the university.)

(The P-13 has no transmitting antenna, although it might
have one on the inside. The unit is shaped like a disk
and is about 2 inches in diameter.)

I got out of the car, and walked into my office here at the
university. My wife called me on the cell phone, and said
she could still hear the signal. I'm on the first floor of
a concrete and steel building, but I am next to some big
windows. Anyway, my wife and I were probably separated
by about 30 feet at that point.

She drove out of the parking lot and lost the signal out in
the university main road. But that is about 100 feet away.

So until she lost the signal (and It might have been more than
100 feet, I don't know) I was just standing in the office holding
this thing in my hand. It was just the Sony IC recorder, playing
back into the P-13 transmitter. I didn't do anything else.
(The units were joined together. There was no connecting cable.)
Now, granted, there are windows here from which the signal
can exit, but when she got out to the main road, those windows
don't help much, because they are not facing the right way.

Now granted, out car radio is very sensitive on FM, but I still
found it interesting that this little transmitter with no external
antenna could go so far. Especially from the first floor of
a concrete and metal building. No external antenna, no
ground plane, no anything.

This little transmitter uses 3 AAA batteries. I use rechargables
that are 1000 mA/hr.

There is one thing about this little P-13 transmitter that is
a major drawback for me, but then again I only paid 12 dollars
for it.

It only operates on 4 FM channels. That's 88.1, 88.3, 88.5, and
88.7.

I have big signals here on 88.1, 88.5, and 88.9. So when i use
the P-13, it has to be on 88.3 or 88.7. A sensitive and selective
radio will get it for some distance, but for a regular radio sitting
in somebody's kitchen, or whatever, you can forget it for use
here in this town. It's just not practical.

It is a very very good link transmitter, through.

So, another random experiment from the Dog Radio Labs.

Best Wishes,
Bruce, DRS2